Various types of liner hangers have been proposed for hanging a liner from a casing string in a well. Most liner hangers are set with slips activated by the liner hanger running tool. Liner hangers with multiple parts pose a significant liability when one or more of the parts becomes loose in the well, thereby disrupting the setting operation and making retrieval difficult. Other liner hangers and running tools cannot perform conventional cementing operations through the running tool before setting the liner hanger in the well.
Other liner hangers have problems supporting heavy liners with the weight of one million pounds or more. Some liner hangers successfully support the liner weight, but do no reliably seal with the casing string. After the liner hanger is set in the well, high fluid pressure in the annulus between the liner and the casing may blow by the liner hanger, thereby defeating its primary purpose. Other liner hangers are not able to obtain burst and/or collapse characteristics equal to that of the casing. A preferred liner hanger maintains a collapse and burst strength at least substantially equal to that of both the casing and the liner.
Liner hangers having gripping elements and packing elements have been expanded to support a liner within the casing. Prior art designs have generally relied upon expansion of the tubular anchor from an elastic state to a plastic state in which the steel lost its fully elasticity or memory. The subsequent relaxation of the energy necessary to maintain the liner hanger at the fully expanded diameter may thus lead to a failure of sealing and/or suspension supporting capability.
Another significant problem with some liner hangers is that the running tool cannot be reliably disengaged from the set liner hanger. This problem with liner hanger technology concerns the desirability to rotate the liner with the work string in the well, then disengage from the work string when the liner hanger has been set to retrieve the running tool from the well. Prior art tools have disengaged from the liner hanger by right-hand rotation of the work string, although some operators for certain applications prefer to avoid right-hand rotation of a work string to release the tool from the set liner.
Publication 2001/0020532A1 discloses a tool for hanging a liner by pipe expansion. U.S. Pat. No. 3,948,321 discloses a reinforcing swage which remains downhole when the tool is retrieved to the surface. U.S. Pat. No. 6,705,395 discloses a radially expanded liner hanger which uses an axially movable annular piston to expand a tubular member.
The disadvantages of the prior art are overcome by the present invention, and an improved liner hanger system and method of setting the liner hanger are hereinafter disclosed.